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Literature survey
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Prepared by M.E. Adams, L. Boniface, T. Nensi and P. Sheard
GENERAL Characterisation of fibres using kerosene and mercury displacement density Kesavan, S.K. Journal of Materials Science Letters Volume 5 No 5 (May 1986) pp 497-498 A theoretical analysis is presented which attempts to establish to magnitude of the errors due to incomplete filling of fibre surface pores and interface/interparticle spaces by kerosene and mercury in displacement density measurements, as applied to the determination of carbon fibre density. Cumulative damage models and multi-stress fatigue life prediction Hwang, W. and Han, K.S. Journal of Composite Materials Vol 20 No 2 (March 1986) pp 125-153 This paper presents an analytical study of cumulative damage during the fatigue of composite materials. Three different models of cumulative damage are defined based on physical variables. Using these models, the cumulative damage is derived as a function of normalized applied stress level and number of fatigue cycles. A comparison of predicted and experimental values of accumulated damage indicates that the model defined using resultant strains gives the best agreement with reality. Design of a composite box beam Bicos, A.S. and Springer, G.S. Journal of Composite Materials Vol 20No 1 (January 1986) pp 86-109 -An analysis is presented for the design of box beams made of fibre-reinforced composites. The analysis provides deflections, bending and torsional stiffnesses, stresses and the conditions for buckling and first-ply failure. The example of a single cell, three-bay, cantilevered box beam is used to demonstrate the selection of a configuration providing a required strength and stiffness at a minimum weight. Geometrically non-linear finite element analysis of imperfect laminated shells Saigal, S., Kapania, R.K. and Yang, T.Y.Journal of Composite Materials Vol 20 No 2 (March 1986) pp 197-214 Formulations and computational procedures are presented for the finite element analysis of imperfect laminated anisotropic thin shells. The shell middle surface is modelled using a general curved shell element with an arbitrary distribution of curvatures. Numerical results are presented for the large deflection and buckling behaviour of a variety of perfect and imperfect shells and plates. Heat conduction in composite materials due to oscillating temperature field Nomura, S. and Chou, T.-W. International Journal of Engineering Science Vo124 No 5 (1986) pp 643-647 A mathematical model is derived for the thermal conductivity and heat capacity in composite materials due to an oscillating temperature field. Algebraic equations are presented for the effective values of these
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quantities when considering the composites as a homogeneous medium; equations are also given for spherical inclusions. The results indicate that the thermal conductivity is not symmetrical with respect to the matrix and inclusion phases. At low frequencies this approach is limited but at high frequencies the quantities depend on the frequency. On the hygrothermomechanical behaviour of a composite material Ene, H.I. International Journal of Engineering Science Vo124 No 5 (1986) pp 841-847 The elastic properties of a composite under the effects of combined moisture and thermal environments have been investigated. The hygrothermomechanical properties of the constituents are considered to be different. Equations for the macroscopic coefficients are deduced and the convergence theorem for the homogenization process is proved. The results obtained are of the same type as those obtained by the classical theory of the mechanisms of Continna. A justification for this rigorous approach is given. Predicting crack growth direction in unidirectional composites Gregory, M.A. and Herakovich, C.T. Journal of Composite Materials Vol 20 No 1 (January 1986) pp 67-85 The effect of anisotropy and biaxial, far-field loading on the direction of crack growth in unidirectional off-axis composite materials has been investigated. An anisotropic crack tip stress analysis is presented using three different criteria to predict the direction of crack extension. By comparing theoretically predicted crack extension directions with those determined experimentally in unidirectional off-axis graphite/epoxy laminates, it was found that only the normal stress ratio criterion correctly predicts the direction of crack extension. The strengths of fiber reinforced composite bends Chang, F.-K. and Springer, G.S. Journal of Composite Materials Vol 20 No 1 (January 1986) pp 30-45 An analysis is presented for calculating the stresses, strains and hence strength of bends in fibre-reinforced composites. Strength is predicted using the Tsai-Hill criterion for in-plane failure and the Chang-Springer criterion for out-of-plane failure. Based on this analysis a computer program was used to evaluate the effects of geometry, ply orientation, and material properties on the strengths and mode of failure of a number of composite bends. Results indicate that stacking sequence is very important in controlling the strength of bends manufactured from composite materials. Vibration and damping analysis of fibre reinforced composite material plates Alam, N. and Asnani, N.T. Journal of Composite Materials Vo120 No 1 (January 1986) pp 2-18 Equations of motion are derived for a laminate plate consisting of an arbitrary number of composite layers. Each layer is considered as a
specially orthotropic material whose elastic properties depend on fibre orientation. A solution is obtained for a simply supported rectangular plate and the damping behaviour analysed using the correspondence principle of linear viscoelasticity. Based on this a computer program is used to determine the fibre orientation that maximizes the resonant frequencies and loss factors of a four-layered angle-ply laminate plate. The calculated variation of resonant frequencies and system loss factors with aspect ratio for two-, four- and six-layered cross-ply laminated plates are also reported.
METAL MA TRICES Aluminium alloy-rice husk ash particle composites Das, S., Dan, T.K. Prasad, S.V. and Rohatgi, P.K. Journal of Materials Science Letters Vol 5 No 5 (May 1986) pp 562-564 In this study, rice husk-ash particles were dispersed in molten aluminium-silicon alloys to study the effect of second phase particles on solidification behaviour of the alloys. Measurements of secondary dendrite arm spacing showed that the structure was coarser with the rice husk particles in the composites than in the base alloy and dendrites were oriented differently inside the particles; it is suggested that the liquid alloy entered the cavity and solidified within the particles as a result of nucleation events separate from the bulk matrix. Effect of porosity and alumina content on the mechanical properties of eompoeast alumininmalloy-alumina particulate composite Ghosh, O.K. and Ray, S. Journal of Materials Science Vo121 No 5 (1986) pp 1667-1674 An AI-4 wt % Mg/alumina composite has been investigated. The reduction in tensile strength due to porosity has been accounted for by an expression containing two parameters: the UTS at zero porosity and a weakening factor. Both are obtained experimentally. The mechanical properties are discussed in terms of void formation and void coalescence with respect to the volume fraction of alumina particles present. The exciting promise of metal-matrix composites Lewis, C.F. Materials Engineering Vol 104 No 5 (May 1986) pp 33-37 This review article looks at the state-of-the-art of metal-matrix composites. A brief history of the development of metal-matrix composites is given, and the various matrix and reinforcement materials are discussed with examples of the fabrication methods used and the products made. The advantages in improved properties over pure alloys is emphasized with examples from industry. Fracture resistance of diamond-reinforced hotpressed Cu/Ni powders Lin, Z. and Queeney, R.A. Powder Metallurgy International (April 1986) pp 76-78 The strength enhancement achieved by metal-
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lizing the diamond prior to blending with the metal matrix powder has been investigated. It was found that prior metallization eliminates the need for carbide-forming additions and thus avoids degrading the toughness of the final metal matrix. With this technique, composite fabrication is a three-step process consisting of coating the diamond with carbide-forming metallics, followed by coating with an alloy compatible with both the carbide and matrix, and finally conventional processing to produce the finished article.
Fracture toughness of duplex fibre-reinforced materials Morley, J.G. Journal of Materials Science Letters Vol 5 No 6 (1986) p 678 This letter clarifies comments made by Mai and Castino (J Mater Sci 19 (1984) p 1638) on the properties of duplex core-sheath reinforcement previously reported by Morley and co-workers. The ability of the duplex fibres to inhibit crack propagation is explained by localized decoupling between the core and sheath, whilst leaving the core intact to carry loads across the faces of the crack. Prestressed fibres can be incorporated into an aluminium matrix; production on a continuous scale is proposed to be practical, and has already been achieved on the laboratory scale. High-strength dispersion hardened niobium for implants Schider, S. The International Journal of Powder Metallurgy Vo122 No 1 (January 196) pp 47-52 The powder metallurgy processing procedures involved in dispersion hardening of niobium are briefly outlined and its use as an implant material discussed. By reviewing the properties and service requirements for implant materials it is concluded that dispersion-hardened niobium is biocompatible, strong and ductile, and yet generally cheaper than other commonly used implant materials. Influence of carbide formation on the strength of carbon fibres on which silicon and titanium have been deposited Honjo, K. and Shindo, A. Journal of Materials Science Vo121 No 6 (1986) pp 2043-2048 The additions of Si and Ti were aimed at overcoming problems in carbon/aluminium composites such as wettability and fibre/matrix reactions. The Si and Ti were chemically vapour deposited on the carbon from SiC14 and TiCI 4 gases respectively. The formation of interface layers is discussed with the optimum conditions established. The strength of the fibre was not degraded by the SiC layer but the strength of the TiC-coated fibre decreased with increasing TiC layer thickness. The TiC layer was deposited much more quickly than the SiC layer. lnterfaeial bond strength in an aluminum alloy 6061-SIC composite Flom, Y and Arsenault, R.J. Materials Science and Engineering Vol 77 (January 1986) pp 191197 An investigation to evaluate the strength of the interfacial bond between SiC and the aluminium alloy 6061 matrix was undertaken. Approximate bounding analysis provided the conditions for separation of the inclusion from the ductile matrix under the local negative pressure (the triaxial tensile stress). The experimental data were analysed to determine the local interfacial stresses at the particle/matrix interfaces. The lower bound value of the bond strength was determined to be at least 1690 MPa. Debonding of SiC particulates from the
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matrix was found to be a rare event. (Authors" abstract)
Linear stress relations for a metal matrix composite sandwich beam ~vith any core material Schoutens, J.E. and Higa, D.I. Journal of Materials Science Vol 21 No 6 (1986) pp 1943-1946 A composite beam consisting of a core sandwiched between an unreinforced upper facing and a reinforced lower facing and subjected to flexural movements is investigated. A model to predict the shear stresses in the interface between the facing material and the core is derived. The results predict that, for a core of low stiffness, the shear stresses will exceed the interface bonding strength, so a stiff core is desirable in a sandwich beam. Mechanical, electrical, and electrical contact properties of Cu-TiO 2 composites Warrier, K.G.K. and Rohatgi, P.K. Powder Metallurgy Vo129 No 1 (1986)pp 65-89 The properties of composites containing 5-20 wt % copper-coated TiO 2 particles prepared by a powder metallurgy route have been investigated. The microstructure, hardness and densities were evaluated at room temperature, the electrical resistivities were measured up to 170°C and life tests were performed to emulate typical light-duty electrical applications. The effect on these properties of varying the titanium content is discussed. For composites containing ~<5 wt % TiO 2 there is little tendency for agglomeration. The authors conclude that the composite is a suitable material for light-duty electrical contacts. The microstructure of Nb3Sn in modified jelly roll superconducting composites Pugh, N.J., Evetts, J.E. and Wallach, E.R. Journal of Materials Science Vo121 No 6 (1986) pp 1914-1918 A TEM study of two superconducting wires with and without 0.8 wt % titanium added to the Ni under different heat treatments has been carried out. The wires were manufactured by the MJR process. Substantial amounts of the AI5 phase were found as a result of premature reactions during fabrication anneals prior to final heat treatments. Increasing heat treatments led to a coarsening of the grains leading to a two-fold layer structure. The addition of titanium resulted in a coarsening of one of the layers. The results are discussed with reference to a model proposed by Cave et al. Multiple fracture of a fibre in a single tungsten fibre/copper matrix composite Ochiai, S. and Osamura, K. ZeitschriJ~ fftr Metallkunde Vol 77 No 4 (April 1986) pp 255-259 A theoretical and experimental study of multiple fibre fracture in a single tungsten fibre/copper matrix composite is presented. It is shown that the number of fractures in the initially continuous fibre increases with increasing applied stress (or strain), the rate of this increase being dependent on the volume fraction of fibre. The length of fibre segments at fracture of the composite increases with fibre volume fraction whilst the overall strain to failure of the composite decreases. The experimental results are shown to be described well by the theoretical model. Properties of composites of 2014 aluminium alloy with Ni-Mo based metallic glass particles Jha, A.K., Upadhyaya, G.S. and Rohatgi, P.K. Journal of Materials Science Vo121 No 5 (1986) pp 1502-1508
The composites were produced using a powder metallurgy route in which the effect of the sintering atmosphere and temperature in production were investigated, and various repressing, re-sintering and age-hardening treatments were conducted. The properties of the composites are discussed with respect to the dimensional behaviour, hardness, electrical resistivity and corrosion behaviour. The effect of including glassy metallic particles was found to improve the properties mentioned by substantial amounts with respect to the base alloy.
Stress distribution of a segmented fibre in loaded single fibre-metal matrix composite Ochai, S. and Osamura, K. Zeitschrifi J~r Metallkunde Vol 77 No 4 (April 1986) pp 249-254 A method is presented to calculate the stress distribution in a segmented single fibre embedded in a metal matrix. It is assumed that the matrix shows linear strain hardening after yielding and that the tensile and shear behaviour of the matrix are independent of each other. Based on this analysis the effect of externally applied stress, fibre length and volume fraction of fbre on the stress distribution in the fibre and on the shear stress distribution at the fibre/matrix interlace are discussed. Work of fracture of unidirectional metal matrix composites subjected to isothermal exposure Kyono, T., Hall, l.W. and Taya, M. Journal of Materials Science Vol 21 No 6 (1986) pp 18791888 The work of fracture Yv of a boron fibrereinforced 1100 aluminium composite has been tested in three-point bend tests. An analytical model to predict 7v under thermal exposure is described. Tests on fibres extracted from the composites before and after exposure have been carried out. Analytical results based on both DiCarlo's model and experimentally measured values for the Weibull parameters gave good agreement with the experimentally measured )'v for the whole range of exposure times. The authors conclude that DiCarlo's model may not be valid for this system where AI203 acts as a reaction barrier between fibres and matrix.
ORGANIC FIBRES Acoustic emission from single and multiple Kevlar-49 filament breaks Hamstad, M.A. and Moore, R.L. Journal of Composite Materials Vol 20 No 1 (January 1986) pp 46-66 Results of acoustic emission (AE) monitored during dry and lubricated bundle and single filament tension tests of Kevlar 49 fibre are reported. The effect of cumulative damage, test fixturing, first w~" second AE sensor hit and friction between fibres has been investigated. It is noted that the failure load for single filament tests does not directly correlate with AE event peak amplitude. Finally, an attempt is made to characterize AE events from multiple filament fractures by reference to AE events from single filament fracture in a bundle. Life time statistics for single Kevlar-49 filaments in creep-rupture Wagner, H.D., Swatz. P. and Phoenix, S.L. Journal of Materials Science Vol 21 No 6 (1986) pp 1868-1878 The creep-rupture behaviour of two spools from the same production lot have been tested. A
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theoretical model based on that of Coleman is described. The experimental results are discussed with respect to the proposed model, their fit to the Weibull distribution, and the results of other workers. The authors have identified three distinct time domains where the lifetime dependence on stress level follows a power law with three different exponents.
RESIN MATRICES Aluminium flake filled conductive plastics for EMI shielding and thermal conductivity Holbrook, A.L The International Journal of Powder Metallurgy Vo122 No I (January 1986) pp 39-45 The use o f a l u m i n i u m flakes for the production of electrically and thermally conductive composites is discussed. The rapid solidification production method used gives flakes with an aspect ratio of 40:1, allowing a conductive network to be set up within the polymer matrix at a much lower loading level and with higher conductivity than traditional powders. The production and use of conductive plastics for EMI shielding and thermal conductivity applications is then outlined. Bi-dimensional compression moulding of superhigh fibre volume fraction composites Ashbee, K.H.G. Journal of Composite Materials Vol 20 No 2 (March 1986) pp 114-124 A bi-dimensional compression moulding apparatus is described for the production of uniaxial fibre-reinforced plastics with fibre volume fractions approaching the theoretical maximum. Using the apparatus described, samples of unidirectional laminates with a 1 cm 2 crosssection have been produced having fibre contents as high as 90% for glass and carbon fibres and higher than 95% for Kevlar fibres. Attention is drawn to the potential offered by these new materials for attaining the ultimate mechanical and electrical properties possible. A comparison of fracture toughness of matrix controlled failure modes: delamination and transverse cracking Lee, S.-M. Journal of Composite Materials Vo120 No 2 (March 1986) pp 185-196 Width tapered double cantilever beam (WTDCB) tests and double torsion (DT) tests have been used to characterize the dclamination and transverse cracking failure modes of a variety of glass and graphite fibre composites. The transverse cracking Gic values determined by the DT method are found to be comparable to the delamination Gic values obtained from the WTDCB method. It is concluded that similar crack tip failure mechanisms exist in both modes. The phenomenon of fibres bridging between crack surfaces and its effect on values of Gic are also discussed. Crack propagation and bifurcation in fibercomposite models: I. Soft-hard-soft sequence of phases Theocaris, P.S., Siarova, M. and Papadopoulos, G.A. Journal of Reinforced Plastics and Composites Vol 5 No 1 (January 1986) pp 23-50 A biphase plate comprising a hard epoxy block moulded into a softer matrix was used to model a hard fibre in a soft resin with mesophase at the interface. Crack propagation and bifurcation bellaviour as a function of epoxy formulation and mechanical properties was investigated by high-speed photography and the method of caustics. As the ratio of the moduli of the phases
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was reduced, it was found that cracks accelerated and attained the critical relative velocities for bifurcation earlier. Voids and inclusions also affected crack branching. Bifurcation appeared to be desirable since it allowed absorption of strain energy and blunted propagating cracks. Cure processes model of organic matrix composites in the presence of vapour release Lee, W.I., Ciriscioli, P.R., Dusi, M.R. and Peterson, D.R. Journal of Reinforced Plastics and Composites Vol 5 No 1 (January 1986)pp 3-8 A model for curing of organic matrix composites in which significant amounts o f v a p o u r are released from the matrix was used to obtain temperature, mass of vapour released/unit volume and degree of cure. Measurements of mass release rate as a function of time and temperature from TGA, and of the role of heat transfer from pressurized and ambient DSC tests, were used in numerical expressions to obtain the required parameters. Description of anisotropic wear rates of polymerbase composites Cyffka, M. and Hornbogen, E. Journal of Materials Science Letters Vol 5 No 4 (April 1986)pp 424--426 Results of measurements of principal wear rates in epoxy composites are compared with calculations from a general formulation for the wear rate in which the sliding path is defined in relation to the symmetry of the material microstructure. Development and testing of bamboo-fibres reinforced plastic composites Jindal, U.C. Journal of Composite Materials Vol 20 No 1 (January 1986) pp 19-29 The tensile strength, impact strength and Young's modulus are reported for bamboo fibre-reinforced plastic (BFRP) composites manufactured using a simple casting technique. The results indicate that the specific ultimate tensile strength of BFRP composites is about eight times that of mild steel. While the mechanical behaviour of these composites is similar to other commonly used composites at low strain rates, the impact strength of BFRP is very low. Diffusion studies on advanced fibre hybrid composites Gopalan, R., Rao, R.M.V.G.K., Murthy, M.V.V. and Dattaguru, B. Journal of Reinforced Plastics and Composites Vol 5 No 1 (January 1986) pp 51-61 Hybrid composites containing combinations of E-glass, graphite and Kevlar fibres in an epoxy matrix were tested to evaluate the effect of mixing impermeable a n d / o r permeable fibres on M m and D x values. Hybrids of impermeable fibres (glass/graphite) showed lower saturated moisture contents and D values compared with Kevlar composites; hybridization of permeable and impermeable fibres influences the diffusion characteristics significantly, so that M and D increase with increasing Vf of Kevlar fibres. A Fickian diffusion model was found to be applicable to these hybrid composites. Edgecoating only had a significant effect on moisture content in the permeable fibre composites. The effect of adsorped water on the dielectric properties of CoCO 3 filled polyethylene composites Banhegyi, G. and Karasz, F.E. Journal of Polymer Science." Polymer Physics Edition Vol 24 No 2 (February 1986)pp 209-228
The dielectric dispersion and loss of a polyethylene-CaCO 3 composite in the ranges 50 Hz-100 kHz and 20-140°C have been investigated. By comparing various theoretical interpretations with the experimental data it is concluded that the observed dispersion and loss are due to adsorbed water at the P E - C a C O 3 interface. The effect of ultra-violet light on mechanical properties of Kevlar 49 composites Larsson, F. Journal of Reinforced Plastics and Composites Vol 5 No 1 (January 1986) pp 19-22 Samples of Kevlar 49/epoxy laminates of varying thickness (1, 2 or 4 layers) were exposed to UV light to totals of 1000 hours and 2000 hours. Mechanical properties after exposure were evaluated; no degradation in tensile elastic modulus and laminate strength was observed, except for the l-layer thick laminate in which strength decreased by ~ 40% after a total of 2000 hours exposure. Fatigue of composites - - fatigue modulus concept and life prediction Hwang, W. and Han, K.S. Journal of Composite Materials Vol 20 No 2 (March 1986) pp 154-165 An analytical study of the fatigue behaviour of glass fibre-reinforced epoxy materials is presented and the concept of 'fatigue modulus' is introduced. A theoretical equation is derived for predicting fatigue life using the fatigue modulus and its degradation rate which is assumed to follow a power function of fatigue cycles. It is demonstrated that this equation predicts the actual fatigue life of glass fibre/ epoxy composite materials more accurately than either S/N curves or Basquin's relation. Finally, an attempt is made to relate fatigue modulus to elastic modulus. Fractography of unidirectional graphite-epoxy as a function of moisture, temperature and specimen quality Clements, L.L. Journal of Materials Science Vol 21 No 6 (1986) pp 1853-1862 Graphite/epoxy composites with either polished or saw cut edges were tested in tension under a variety of environmental conditions. The specimen quality was determined by previous mechanical testing on two batches of prepreg; batch A giving normal properties while batch B gave anomalous properties. The effects of the testing variables are discussed with respect to the fracture morphology. A distinctive type of morphology was identified with defective specimens. With increasing temperature (dry) and increasing moisture content (25°C) the tensile strength increased due to decreased flaw sensitivity, but under hot wet conditions interfacial debonding increased. Fracture and fatigue of short glass-fibre reinforced PTFE composites Voss, H. and Friedrich, K. Journal of Materials Science Letters Vol 5 No 5 (May 1986) pp 569-572 This is an investigation into fracture toughness and fatigue crack growth in PTFE and three short fibre composites with different Vf. Notched bulk PTFE showed a low static and fatigue toughness; addition of fibres further reduced toughness and promoted fatigue crack growth. A 'microstructural efficiency factor' was used to account for the effect of composite microstructure on crack propagation rate. Fretting fatigue of polyester resin and its glass fibre mat composites Friedrich, K. Journal of Materials Science Vo121 No 5 (1986) pp 1700-1706
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An unsaturated polyester containing ~ 50% CaCO 3 particles and reinforced with either 27 wt % or 37 wt % glass mat have been investigated. Static tensile, fretting fatigue and wear tests have been carried out and the results are discussed in terms of the failure processes involved. The conclusions are that the presence of the glass improves the general mechanical properties but that the endurance limit is reduced by the fretting action and is a function of the fibre orientation to the fretting direction.
Glass reinforced plastic pipe bend subjected to vacuum and flexure Kitching, R. and Myler, P. International Journal of Mechanical Science Vo128 No 3 (1986) pp 179192 A90 ° pipe bend made of E-glass chopped strand mat and polyester resin has been subjected to vacuum only and in-plane and out-of-phase flexure with and without vacuum. The derived stress distributions were compared with theoretical estimates such as the MITRE computer program. Agreements with the theory are good at low external pressures but deviate at higher pressures when deflections are no longer small. The theories also do not predict maximum stress very accurately. The authors conclude that the flexibility of a pipe bend is increased by a vacuum. The flexibility and stress concentration factors can for practical purposes be predicted by MITRE but under certain conditions of vacuum and flexure instabilities may occur, Interracial effects in carbon-epoxies. Part 3. Toughness with short fibres Sanadi, A.R. and Piggot, M.R. Journal of Materials Science Vol 21 No 5 (1986) pp 16421646 The work of fracture of a carbon/epoxy composite has been studied using using the Izod impact test. Four different surface treatments were given to the carbon fibres to alter their critical length. The results, which are discussed with respect to current theoretical ideas, do not agree with the theories giving lower values for the work of fracture. This is attributed to the mode of failure in these composites, in which debonding is inhibited. Long/short fiber reinforced thermoplastics Gore, C.R. Cuff, G. and Cianelli, D.A.Materials Engineering Vol 103 No 3 (March 1985) pp 4750 A new long fibre/thermoplastic is described which can be processed by conventional short fibre processing techniques. The product has improved fibre/matrix banding which can give 10-20 times the resultant fibre length of short
fibre composites. The melt-processable pellets are produced by a pultrusion process. Improved impact, stiffness, high temperature, and other properties are claimed. Tests on finished components substantiate the claims.
Progressive fracture of fiber composites Irvine, T.B. and Ginty, C.A.Journal of Composite Materials Vo120 No 2 (March 1986) pp 166-184 The use of real-time ultrasonic C-scan (RUSCAN) and composite durability structural analysis (CODSTRAN) computer code is described for determining progressive composite fracture in graphite/epoxy angle-plied laminates. Using these techniques in conjunction with scanning electron microscopy the durability and failure mechanisms in graphite/epoxy composites have been studied. It is concluded that the combination of RUSCAN/CODSTRAN is an effective method of studying progressive fracture of composites. The reflection properties of debonded fibres in GRP Sargent, J.P. and Gass, P.A.Journal of Physics D: Applied Physics Vol 19 (1986)pp 897-907 The microscopic reflection optics of debonded glass fibres have been modelled using an ultrasound analogue, a Schlieren system. The effects seen in the model and in practice have been compared with a theoretical model. The results are discussed in terms of describing the geometry of the debond. SEM observations on the origins of toughness of natural fibre-polyester composites Sanadi, A.R., Prasad, S.V. and Rohatgi, P.K. Journal of Materials Science Letters Vo[ 5 No 4 (April 1986) pp 395-396 This work investigates the mechanics of energy absorption in impact of sunhemp fibre/polyester composites by SEM observations after [zod toughness tests. Fibre fracture modes include fibril pull-out, plastic flow of the ligninhemicellulose matrix, plastic deformation of fibrils, fibre splitting and diversion of the crack at the fibril/fibril interface. These fracture mechanisms are considered to contribute to the high toughness of this composite. Some electron microscope observations of longitudinal splitting from surface flaws in Kevlar 29 Wagner, H.D.Journal of Materials Science Letters Vol 5 No 4 (April 1986) pp 439-440 This work describes observations of splitting damage in Kevlar 29 thermoplastic composites. Fibrils were seen to peel away from the fibre surface leaving axial grooves on the surface.
The splitting phenomenon is modelled using a simple theoretical calculation for the stress required to initiate splitting from the root of a semi-circular surface defect.
Some properties of a condensed polynuelear aromatic resin (COPNA) as a binder for carbon fibre composites Otani, S.. Raskovic, V., Oya. A, and Kojima, A Journal of Materials Science Vol 21 No 6 (1986) pp 2027-2032 The thermosetting resin (COPNA) was prepared from a mixture of pyrene, phenanthrene and 1,4-benzene dimethanol. Mechanical properties of carbon fibre/COPNA, carbon fibre/COPNA B-staged and carbon/carbon composites were evaluated. The results showed that the COPNA resin composites maintain their properties after heating in air for long periods at temperatures of 523 K and 573 K. The properties were also similar to epoxy resin composites. The authors conclude that COPNA is worth studying for its heat-resistance properties. Three-dimensional moisture diffusion in graphite/epoxy laminates Blikstad, M. Journal of Reinforced Plastics and Composites Vol 5 No 1 (Janua O' 1986) pp 9-18 Graphite/epoxy specimens of varying configurations were used to investigate diffusivity to and along the fiber direction: they were exposed at RH of 70% and 98% at323 K. Diffusivity parallel to the fibres was approximately 10 times greater than generally found in laminates: this was due to the geometrical effect of the fibre orientation and the enhancement of diffusion along the fibre/matrix interface. The temperature dependence of diffusion (activation energy in an Arrhenius analysis) was lowest for diffusion along the fibre direction. A three-dimensional Fickian model for moisture absorption gave good agreement with experimental values. Wollastonite reinforced polypropylene composites: dynamic and steady state melt flow behaviour Shenoy. A.V. and Saini, D.R Journal of Reinforced Plastics and Composties Vol 5 No 1 (January 1986) pp 62-73 Dynamic and steady-state rheological properties of a composite of polypropylene and wollastonite were studied at 22l)°C: complex viscosity, storage modulus and loss modulus were measured over the frequency range 0.1-100 rad s 1, as well as the steady-shear viscosity. The experimentatl results were fitted to theoretical rheological predictions and allowed estimation of theological characteristics at different filler loadings.
OFI A2tIt Abstracts of British Patents are prepared by Dr F.R. Jones, Department of Ceramics, Glasses and Polymers, University of Sheffield, UK
UK PATENTS COMPONENTS Stackable long-term storage container, preferably for radioactive waste (Kernforschungszentrum Karlsruhe GmbH, FRG) GB 2 163 382,4 (20 February 1986) A GRP insert is used in a radioactive waste
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container to give corrosion protection.
Lightweight concrete roof tiles (The Marley Roof Tile Company, UK) GB2163 421A (26 February 1986) Concrete tiles with higher specific flexural strength are produced when a non-thixotropic silica fume (and dispersing agent) is included in the composition. Composite concrete huilding panel (McNeil, A. of Scotland) GB 2 164 072A
(12 March 1986) A panel consisting of acrylic acid copolymer modified G RC surfaces with a cellular concrete core is described. Polyacrylonitrile fiber with high strength and modulus (Japan Exlan Company Ltd, Japan) GB 2 165 484,4 (16 April 1986) The title fibre can be used as tyre-cord composites or as a carbon fibre precursor. It is spun
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re survev I
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Prepared by M.E. Adams, L. Boniface, T. Nensi and P. Sheard
GENERAL Characterisation of fibres using kerosene and mercury displacement density Kesavan, S.K. Journal of Materials Science Letters Volume 5 No 5 (May 1986) pp 497-498 A theoretical analysis is presented which attempts to establish to magnitude of the errors due to incomplete filling of fibre surface pores and interface/interparticle spaces by kerosene and mercury in displacement density measurements, as applied to the determination of carbon fibre density. Cumulative damage models and multi-stress fatigue life prediction Hwang, W. and Han, K.S. Journal of Composite Materials Vol 20 No 2 (March 1986) pp 125-153 This paper presents an analytical study of cumulative damage during the fatigue of composite materials. Three different models of cumulative damage are defined based on physical variables. Using these models, the cumulative damage is derived as a function of normalized applied stress level and number of fatigue cycles. A comparison of predicted and experimental values of accumulated damage indicates that the model defined using resultant strains gives the best agreement with reality. Design of a composite box beam Bicos, A.S. and Springer, G.S. Journal of Composite Materials Vol 20No 1 (January 1986) pp 86-109 -An analysis is presented for the design of box beams made of fibre-reinforced composites. The analysis provides deflections, bending and torsional stiffnesses, stresses and the conditions for buckling and first-ply failure. The example of a single cell, three-bay, cantilevered box beam is used to demonstrate the selection of a configuration providing a required strength and stiffness at a minimum weight. Geometrically non-linear finite element analysis of imperfect laminated shells Saigal, S., Kapania, R.K. and Yang, T.Y.Journal of Composite Materials Vol 20 No 2 (March 1986) pp 197-214 Formulations and computational procedures are presented for the finite element analysis of imperfect laminated anisotropic thin shells. The shell middle surface is modelled using a general curved shell element with an arbitrary distribution of curvatures. Numerical results are presented for the large deflection and buckling behaviour of a variety of perfect and imperfect shells and plates. Heat conduction in composite materials due to oscillating temperature field Nomura, S. and Chou, T.-W. International Journal of Engineering Science Vo124 No 5 (1986) pp 643-647 A mathematical model is derived for the thermal conductivity and heat capacity in composite materials due to an oscillating temperature field. Algebraic equations are presented for the effective values of these
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quantities when considering the composites as a homogeneous medium; equations are also given for spherical inclusions. The results indicate that the thermal conductivity is not symmetrical with respect to the matrix and inclusion phases. At low frequencies this approach is limited but at high frequencies the quantities depend on the frequency. On the hygrothermomechanical behaviour of a composite material Ene, H.I. International Journal of Engineering Science Vo124 No 5 (1986) pp 841-847 The elastic properties of a composite under the effects of combined moisture and thermal environments have been investigated. The hygrothermomechanical properties of the constituents are considered to be different. Equations for the macroscopic coefficients are deduced and the convergence theorem for the homogenization process is proved. The results obtained are of the same type as those obtained by the classical theory of the mechanisms of Continna. A justification for this rigorous approach is given. Predicting crack growth direction in unidirectional composites Gregory, M.A. and Herakovich, C.T. Journal of Composite Materials Vol 20 No 1 (January 1986) pp 67-85 The effect of anisotropy and biaxial, far-field loading on the direction of crack growth in unidirectional off-axis composite materials has been investigated. An anisotropic crack tip stress analysis is presented using three different criteria to predict the direction of crack extension. By comparing theoretically predicted crack extension directions with those determined experimentally in unidirectional off-axis graphite/epoxy laminates, it was found that only the normal stress ratio criterion correctly predicts the direction of crack extension. The strengths of fiber reinforced composite bends Chang, F.-K. and Springer, G.S. Journal of Composite Materials Vol 20 No 1 (January 1986) pp 30-45 An analysis is presented for calculating the stresses, strains and hence strength of bends in fibre-reinforced composites. Strength is predicted using the Tsai-Hill criterion for in-plane failure and the Chang-Springer criterion for out-of-plane failure. Based on this analysis a computer program was used to evaluate the effects of geometry, ply orientation, and material properties on the strengths and mode of failure of a number of composite bends. Results indicate that stacking sequence is very important in controlling the strength of bends manufactured from composite materials. Vibration and damping analysis of fibre reinforced composite material plates Alam, N. and Asnani, N.T. Journal of Composite Materials Vo120 No 1 (January 1986) pp 2-18 Equations of motion are derived for a laminate plate consisting of an arbitrary number of composite layers. Each layer is considered as a
specially orthotropic material whose elastic properties depend on fibre orientation. A solution is obtained for a simply supported rectangular plate and the damping behaviour analysed using the correspondence principle of linear viscoelasticity. Based on this a computer program is used to determine the fibre orientation that maximizes the resonant frequencies and loss factors of a four-layered angle-ply laminate plate. The calculated variation of resonant frequencies and system loss factors with aspect ratio for two-, four- and six-layered cross-ply laminated plates are also reported.
METAL MA TRICES Aluminium alloy-rice husk ash particle composites Das, S., Dan, T.K. Prasad, S.V. and Rohatgi, P.K. Journal of Materials Science Letters Vol 5 No 5 (May 1986) pp 562-564 In this study, rice husk-ash particles were dispersed in molten aluminium-silicon alloys to study the effect of second phase particles on solidification behaviour of the alloys. Measurements of secondary dendrite arm spacing showed that the structure was coarser with the rice husk particles in the composites than in the base alloy and dendrites were oriented differently inside the particles; it is suggested that the liquid alloy entered the cavity and solidified within the particles as a result of nucleation events separate from the bulk matrix. Effect of porosity and alumina content on the mechanical properties of eompoeast alumininmalloy-alumina particulate composite Ghosh, O.K. and Ray, S. Journal of Materials Science Vo121 No 5 (1986) pp 1667-1674 An AI-4 wt % Mg/alumina composite has been investigated. The reduction in tensile strength due to porosity has been accounted for by an expression containing two parameters: the UTS at zero porosity and a weakening factor. Both are obtained experimentally. The mechanical properties are discussed in terms of void formation and void coalescence with respect to the volume fraction of alumina particles present. The exciting promise of metal-matrix composites Lewis, C.F. Materials Engineering Vol 104 No 5 (May 1986) pp 33-37 This review article looks at the state-of-the-art of metal-matrix composites. A brief history of the development of metal-matrix composites is given, and the various matrix and reinforcement materials are discussed with examples of the fabrication methods used and the products made. The advantages in improved properties over pure alloys is emphasized with examples from industry. Fracture resistance of diamond-reinforced hotpressed Cu/Ni powders Lin, Z. and Queeney, R.A. Powder Metallurgy International (April 1986) pp 76-78 The strength enhancement achieved by metal-
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lizing the diamond prior to blending with the metal matrix powder has been investigated. It was found that prior metallization eliminates the need for carbide-forming additions and thus avoids degrading the toughness of the final metal matrix. With this technique, composite fabrication is a three-step process consisting of coating the diamond with carbide-forming metallics, followed by coating with an alloy compatible with both the carbide and matrix, and finally conventional processing to produce the finished article.
Fracture toughness of duplex fibre-reinforced materials Morley, J.G. Journal of Materials Science Letters Vol 5 No 6 (1986) p 678 This letter clarifies comments made by Mai and Castino (J Mater Sci 19 (1984) p 1638) on the properties of duplex core-sheath reinforcement previously reported by Morley and co-workers. The ability of the duplex fibres to inhibit crack propagation is explained by localized decoupling between the core and sheath, whilst leaving the core intact to carry loads across the faces of the crack. Prestressed fibres can be incorporated into an aluminium matrix; production on a continuous scale is proposed to be practical, and has already been achieved on the laboratory scale. High-strength dispersion hardened niobium for implants Schider, S. The International Journal of Powder Metallurgy Vo122 No 1 (January 196) pp 47-52 The powder metallurgy processing procedures involved in dispersion hardening of niobium are briefly outlined and its use as an implant material discussed. By reviewing the properties and service requirements for implant materials it is concluded that dispersion-hardened niobium is biocompatible, strong and ductile, and yet generally cheaper than other commonly used implant materials. Influence of carbide formation on the strength of carbon fibres on which silicon and titanium have been deposited Honjo, K. and Shindo, A. Journal of Materials Science Vo121 No 6 (1986) pp 2043-2048 The additions of Si and Ti were aimed at overcoming problems in carbon/aluminium composites such as wettability and fibre/matrix reactions. The Si and Ti were chemically vapour deposited on the carbon from SiC14 and TiCI 4 gases respectively. The formation of interface layers is discussed with the optimum conditions established. The strength of the fibre was not degraded by the SiC layer but the strength of the TiC-coated fibre decreased with increasing TiC layer thickness. The TiC layer was deposited much more quickly than the SiC layer. lnterfaeial bond strength in an aluminum alloy 6061-SIC composite Flom, Y and Arsenault, R.J. Materials Science and Engineering Vol 77 (January 1986) pp 191197 An investigation to evaluate the strength of the interfacial bond between SiC and the aluminium alloy 6061 matrix was undertaken. Approximate bounding analysis provided the conditions for separation of the inclusion from the ductile matrix under the local negative pressure (the triaxial tensile stress). The experimental data were analysed to determine the local interfacial stresses at the particle/matrix interfaces. The lower bound value of the bond strength was determined to be at least 1690 MPa. Debonding of SiC particulates from the
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matrix was found to be a rare event. (Authors" abstract)
Linear stress relations for a metal matrix composite sandwich beam ~vith any core material Schoutens, J.E. and Higa, D.I. Journal of Materials Science Vol 21 No 6 (1986) pp 1943-1946 A composite beam consisting of a core sandwiched between an unreinforced upper facing and a reinforced lower facing and subjected to flexural movements is investigated. A model to predict the shear stresses in the interface between the facing material and the core is derived. The results predict that, for a core of low stiffness, the shear stresses will exceed the interface bonding strength, so a stiff core is desirable in a sandwich beam. Mechanical, electrical, and electrical contact properties of Cu-TiO 2 composites Warrier, K.G.K. and Rohatgi, P.K. Powder Metallurgy Vo129 No 1 (1986)pp 65-89 The properties of composites containing 5-20 wt % copper-coated TiO 2 particles prepared by a powder metallurgy route have been investigated. The microstructure, hardness and densities were evaluated at room temperature, the electrical resistivities were measured up to 170°C and life tests were performed to emulate typical light-duty electrical applications. The effect on these properties of varying the titanium content is discussed. For composites containing ~<5 wt % TiO 2 there is little tendency for agglomeration. The authors conclude that the composite is a suitable material for light-duty electrical contacts. The microstructure of Nb3Sn in modified jelly roll superconducting composites Pugh, N.J., Evetts, J.E. and Wallach, E.R. Journal of Materials Science Vo121 No 6 (1986) pp 1914-1918 A TEM study of two superconducting wires with and without 0.8 wt % titanium added to the Ni under different heat treatments has been carried out. The wires were manufactured by the MJR process. Substantial amounts of the AI5 phase were found as a result of premature reactions during fabrication anneals prior to final heat treatments. Increasing heat treatments led to a coarsening of the grains leading to a two-fold layer structure. The addition of titanium resulted in a coarsening of one of the layers. The results are discussed with reference to a model proposed by Cave et al. Multiple fracture of a fibre in a single tungsten fibre/copper matrix composite Ochiai, S. and Osamura, K. ZeitschriJ~ fftr Metallkunde Vol 77 No 4 (April 1986) pp 255-259 A theoretical and experimental study of multiple fibre fracture in a single tungsten fibre/copper matrix composite is presented. It is shown that the number of fractures in the initially continuous fibre increases with increasing applied stress (or strain), the rate of this increase being dependent on the volume fraction of fibre. The length of fibre segments at fracture of the composite increases with fibre volume fraction whilst the overall strain to failure of the composite decreases. The experimental results are shown to be described well by the theoretical model. Properties of composites of 2014 aluminium alloy with Ni-Mo based metallic glass particles Jha, A.K., Upadhyaya, G.S. and Rohatgi, P.K. Journal of Materials Science Vo121 No 5 (1986) pp 1502-1508
The composites were produced using a powder metallurgy route in which the effect of the sintering atmosphere and temperature in production were investigated, and various repressing, re-sintering and age-hardening treatments were conducted. The properties of the composites are discussed with respect to the dimensional behaviour, hardness, electrical resistivity and corrosion behaviour. The effect of including glassy metallic particles was found to improve the properties mentioned by substantial amounts with respect to the base alloy.
Stress distribution of a segmented fibre in loaded single fibre-metal matrix composite Ochai, S. and Osamura, K. Zeitschrifi J~r Metallkunde Vol 77 No 4 (April 1986) pp 249-254 A method is presented to calculate the stress distribution in a segmented single fibre embedded in a metal matrix. It is assumed that the matrix shows linear strain hardening after yielding and that the tensile and shear behaviour of the matrix are independent of each other. Based on this analysis the effect of externally applied stress, fibre length and volume fraction of fbre on the stress distribution in the fibre and on the shear stress distribution at the fibre/matrix interlace are discussed. Work of fracture of unidirectional metal matrix composites subjected to isothermal exposure Kyono, T., Hall, l.W. and Taya, M. Journal of Materials Science Vol 21 No 6 (1986) pp 18791888 The work of fracture Yv of a boron fibrereinforced 1100 aluminium composite has been tested in three-point bend tests. An analytical model to predict 7v under thermal exposure is described. Tests on fibres extracted from the composites before and after exposure have been carried out. Analytical results based on both DiCarlo's model and experimentally measured values for the Weibull parameters gave good agreement with the experimentally measured )'v for the whole range of exposure times. The authors conclude that DiCarlo's model may not be valid for this system where AI203 acts as a reaction barrier between fibres and matrix.
ORGANIC FIBRES Acoustic emission from single and multiple Kevlar-49 filament breaks Hamstad, M.A. and Moore, R.L. Journal of Composite Materials Vol 20 No 1 (January 1986) pp 46-66 Results of acoustic emission (AE) monitored during dry and lubricated bundle and single filament tension tests of Kevlar 49 fibre are reported. The effect of cumulative damage, test fixturing, first w~" second AE sensor hit and friction between fibres has been investigated. It is noted that the failure load for single filament tests does not directly correlate with AE event peak amplitude. Finally, an attempt is made to characterize AE events from multiple filament fractures by reference to AE events from single filament fracture in a bundle. Life time statistics for single Kevlar-49 filaments in creep-rupture Wagner, H.D., Swatz. P. and Phoenix, S.L. Journal of Materials Science Vol 21 No 6 (1986) pp 1868-1878 The creep-rupture behaviour of two spools from the same production lot have been tested. A
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theoretical model based on that of Coleman is described. The experimental results are discussed with respect to the proposed model, their fit to the Weibull distribution, and the results of other workers. The authors have identified three distinct time domains where the lifetime dependence on stress level follows a power law with three different exponents.
RESIN MATRICES Aluminium flake filled conductive plastics for EMI shielding and thermal conductivity Holbrook, A.L The International Journal of Powder Metallurgy Vo122 No I (January 1986) pp 39-45 The use o f a l u m i n i u m flakes for the production of electrically and thermally conductive composites is discussed. The rapid solidification production method used gives flakes with an aspect ratio of 40:1, allowing a conductive network to be set up within the polymer matrix at a much lower loading level and with higher conductivity than traditional powders. The production and use of conductive plastics for EMI shielding and thermal conductivity applications is then outlined. Bi-dimensional compression moulding of superhigh fibre volume fraction composites Ashbee, K.H.G. Journal of Composite Materials Vol 20 No 2 (March 1986) pp 114-124 A bi-dimensional compression moulding apparatus is described for the production of uniaxial fibre-reinforced plastics with fibre volume fractions approaching the theoretical maximum. Using the apparatus described, samples of unidirectional laminates with a 1 cm 2 crosssection have been produced having fibre contents as high as 90% for glass and carbon fibres and higher than 95% for Kevlar fibres. Attention is drawn to the potential offered by these new materials for attaining the ultimate mechanical and electrical properties possible. A comparison of fracture toughness of matrix controlled failure modes: delamination and transverse cracking Lee, S.-M. Journal of Composite Materials Vo120 No 2 (March 1986) pp 185-196 Width tapered double cantilever beam (WTDCB) tests and double torsion (DT) tests have been used to characterize the dclamination and transverse cracking failure modes of a variety of glass and graphite fibre composites. The transverse cracking Gic values determined by the DT method are found to be comparable to the delamination Gic values obtained from the WTDCB method. It is concluded that similar crack tip failure mechanisms exist in both modes. The phenomenon of fibres bridging between crack surfaces and its effect on values of Gic are also discussed. Crack propagation and bifurcation in fibercomposite models: I. Soft-hard-soft sequence of phases Theocaris, P.S., Siarova, M. and Papadopoulos, G.A. Journal of Reinforced Plastics and Composites Vol 5 No 1 (January 1986) pp 23-50 A biphase plate comprising a hard epoxy block moulded into a softer matrix was used to model a hard fibre in a soft resin with mesophase at the interface. Crack propagation and bifurcation bellaviour as a function of epoxy formulation and mechanical properties was investigated by high-speed photography and the method of caustics. As the ratio of the moduli of the phases
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was reduced, it was found that cracks accelerated and attained the critical relative velocities for bifurcation earlier. Voids and inclusions also affected crack branching. Bifurcation appeared to be desirable since it allowed absorption of strain energy and blunted propagating cracks. Cure processes model of organic matrix composites in the presence of vapour release Lee, W.I., Ciriscioli, P.R., Dusi, M.R. and Peterson, D.R. Journal of Reinforced Plastics and Composites Vol 5 No 1 (January 1986)pp 3-8 A model for curing of organic matrix composites in which significant amounts o f v a p o u r are released from the matrix was used to obtain temperature, mass of vapour released/unit volume and degree of cure. Measurements of mass release rate as a function of time and temperature from TGA, and of the role of heat transfer from pressurized and ambient DSC tests, were used in numerical expressions to obtain the required parameters. Description of anisotropic wear rates of polymerbase composites Cyffka, M. and Hornbogen, E. Journal of Materials Science Letters Vol 5 No 4 (April 1986)pp 424--426 Results of measurements of principal wear rates in epoxy composites are compared with calculations from a general formulation for the wear rate in which the sliding path is defined in relation to the symmetry of the material microstructure. Development and testing of bamboo-fibres reinforced plastic composites Jindal, U.C. Journal of Composite Materials Vol 20 No 1 (January 1986) pp 19-29 The tensile strength, impact strength and Young's modulus are reported for bamboo fibre-reinforced plastic (BFRP) composites manufactured using a simple casting technique. The results indicate that the specific ultimate tensile strength of BFRP composites is about eight times that of mild steel. While the mechanical behaviour of these composites is similar to other commonly used composites at low strain rates, the impact strength of BFRP is very low. Diffusion studies on advanced fibre hybrid composites Gopalan, R., Rao, R.M.V.G.K., Murthy, M.V.V. and Dattaguru, B. Journal of Reinforced Plastics and Composites Vol 5 No 1 (January 1986) pp 51-61 Hybrid composites containing combinations of E-glass, graphite and Kevlar fibres in an epoxy matrix were tested to evaluate the effect of mixing impermeable a n d / o r permeable fibres on M m and D x values. Hybrids of impermeable fibres (glass/graphite) showed lower saturated moisture contents and D values compared with Kevlar composites; hybridization of permeable and impermeable fibres influences the diffusion characteristics significantly, so that M and D increase with increasing Vf of Kevlar fibres. A Fickian diffusion model was found to be applicable to these hybrid composites. Edgecoating only had a significant effect on moisture content in the permeable fibre composites. The effect of adsorped water on the dielectric properties of CoCO 3 filled polyethylene composites Banhegyi, G. and Karasz, F.E. Journal of Polymer Science." Polymer Physics Edition Vol 24 No 2 (February 1986)pp 209-228
The dielectric dispersion and loss of a polyethylene-CaCO 3 composite in the ranges 50 Hz-100 kHz and 20-140°C have been investigated. By comparing various theoretical interpretations with the experimental data it is concluded that the observed dispersion and loss are due to adsorbed water at the P E - C a C O 3 interface. The effect of ultra-violet light on mechanical properties of Kevlar 49 composites Larsson, F. Journal of Reinforced Plastics and Composites Vol 5 No 1 (January 1986) pp 19-22 Samples of Kevlar 49/epoxy laminates of varying thickness (1, 2 or 4 layers) were exposed to UV light to totals of 1000 hours and 2000 hours. Mechanical properties after exposure were evaluated; no degradation in tensile elastic modulus and laminate strength was observed, except for the l-layer thick laminate in which strength decreased by ~ 40% after a total of 2000 hours exposure. Fatigue of composites - - fatigue modulus concept and life prediction Hwang, W. and Han, K.S. Journal of Composite Materials Vol 20 No 2 (March 1986) pp 154-165 An analytical study of the fatigue behaviour of glass fibre-reinforced epoxy materials is presented and the concept of 'fatigue modulus' is introduced. A theoretical equation is derived for predicting fatigue life using the fatigue modulus and its degradation rate which is assumed to follow a power function of fatigue cycles. It is demonstrated that this equation predicts the actual fatigue life of glass fibre/ epoxy composite materials more accurately than either S/N curves or Basquin's relation. Finally, an attempt is made to relate fatigue modulus to elastic modulus. Fractography of unidirectional graphite-epoxy as a function of moisture, temperature and specimen quality Clements, L.L. Journal of Materials Science Vol 21 No 6 (1986) pp 1853-1862 Graphite/epoxy composites with either polished or saw cut edges were tested in tension under a variety of environmental conditions. The specimen quality was determined by previous mechanical testing on two batches of prepreg; batch A giving normal properties while batch B gave anomalous properties. The effects of the testing variables are discussed with respect to the fracture morphology. A distinctive type of morphology was identified with defective specimens. With increasing temperature (dry) and increasing moisture content (25°C) the tensile strength increased due to decreased flaw sensitivity, but under hot wet conditions interfacial debonding increased. Fracture and fatigue of short glass-fibre reinforced PTFE composites Voss, H. and Friedrich, K. Journal of Materials Science Letters Vol 5 No 5 (May 1986) pp 569-572 This is an investigation into fracture toughness and fatigue crack growth in PTFE and three short fibre composites with different Vf. Notched bulk PTFE showed a low static and fatigue toughness; addition of fibres further reduced toughness and promoted fatigue crack growth. A 'microstructural efficiency factor' was used to account for the effect of composite microstructure on crack propagation rate. Fretting fatigue of polyester resin and its glass fibre mat composites Friedrich, K. Journal of Materials Science Vo121 No 5 (1986) pp 1700-1706
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An unsaturated polyester containing ~ 50% CaCO 3 particles and reinforced with either 27 wt % or 37 wt % glass mat have been investigated. Static tensile, fretting fatigue and wear tests have been carried out and the results are discussed in terms of the failure processes involved. The conclusions are that the presence of the glass improves the general mechanical properties but that the endurance limit is reduced by the fretting action and is a function of the fibre orientation to the fretting direction.
Glass reinforced plastic pipe bend subjected to vacuum and flexure Kitching, R. and Myler, P. International Journal of Mechanical Science Vo128 No 3 (1986) pp 179192 A90 ° pipe bend made of E-glass chopped strand mat and polyester resin has been subjected to vacuum only and in-plane and out-of-phase flexure with and without vacuum. The derived stress distributions were compared with theoretical estimates such as the MITRE computer program. Agreements with the theory are good at low external pressures but deviate at higher pressures when deflections are no longer small. The theories also do not predict maximum stress very accurately. The authors conclude that the flexibility of a pipe bend is increased by a vacuum. The flexibility and stress concentration factors can for practical purposes be predicted by MITRE but under certain conditions of vacuum and flexure instabilities may occur, Interracial effects in carbon-epoxies. Part 3. Toughness with short fibres Sanadi, A.R. and Piggot, M.R. Journal of Materials Science Vol 21 No 5 (1986) pp 16421646 The work of fracture of a carbon/epoxy composite has been studied using using the Izod impact test. Four different surface treatments were given to the carbon fibres to alter their critical length. The results, which are discussed with respect to current theoretical ideas, do not agree with the theories giving lower values for the work of fracture. This is attributed to the mode of failure in these composites, in which debonding is inhibited. Long/short fiber reinforced thermoplastics Gore, C.R. Cuff, G. and Cianelli, D.A.Materials Engineering Vol 103 No 3 (March 1985) pp 4750 A new long fibre/thermoplastic is described which can be processed by conventional short fibre processing techniques. The product has improved fibre/matrix banding which can give 10-20 times the resultant fibre length of short
fibre composites. The melt-processable pellets are produced by a pultrusion process. Improved impact, stiffness, high temperature, and other properties are claimed. Tests on finished components substantiate the claims.
Progressive fracture of fiber composites Irvine, T.B. and Ginty, C.A.Journal of Composite Materials Vo120 No 2 (March 1986) pp 166-184 The use of real-time ultrasonic C-scan (RUSCAN) and composite durability structural analysis (CODSTRAN) computer code is described for determining progressive composite fracture in graphite/epoxy angle-plied laminates. Using these techniques in conjunction with scanning electron microscopy the durability and failure mechanisms in graphite/epoxy composites have been studied. It is concluded that the combination of RUSCAN/CODSTRAN is an effective method of studying progressive fracture of composites. The reflection properties of debonded fibres in GRP Sargent, J.P. and Gass, P.A.Journal of Physics D: Applied Physics Vol 19 (1986)pp 897-907 The microscopic reflection optics of debonded glass fibres have been modelled using an ultrasound analogue, a Schlieren system. The effects seen in the model and in practice have been compared with a theoretical model. The results are discussed in terms of describing the geometry of the debond. SEM observations on the origins of toughness of natural fibre-polyester composites Sanadi, A.R., Prasad, S.V. and Rohatgi, P.K. Journal of Materials Science Letters Vo[ 5 No 4 (April 1986) pp 395-396 This work investigates the mechanics of energy absorption in impact of sunhemp fibre/polyester composites by SEM observations after [zod toughness tests. Fibre fracture modes include fibril pull-out, plastic flow of the ligninhemicellulose matrix, plastic deformation of fibrils, fibre splitting and diversion of the crack at the fibril/fibril interface. These fracture mechanisms are considered to contribute to the high toughness of this composite. Some electron microscope observations of longitudinal splitting from surface flaws in Kevlar 29 Wagner, H.D.Journal of Materials Science Letters Vol 5 No 4 (April 1986) pp 439-440 This work describes observations of splitting damage in Kevlar 29 thermoplastic composites. Fibrils were seen to peel away from the fibre surface leaving axial grooves on the surface.
The splitting phenomenon is modelled using a simple theoretical calculation for the stress required to initiate splitting from the root of a semi-circular surface defect.
Some properties of a condensed polynuelear aromatic resin (COPNA) as a binder for carbon fibre composites Otani, S.. Raskovic, V., Oya. A, and Kojima, A Journal of Materials Science Vol 21 No 6 (1986) pp 2027-2032 The thermosetting resin (COPNA) was prepared from a mixture of pyrene, phenanthrene and 1,4-benzene dimethanol. Mechanical properties of carbon fibre/COPNA, carbon fibre/COPNA B-staged and carbon/carbon composites were evaluated. The results showed that the COPNA resin composites maintain their properties after heating in air for long periods at temperatures of 523 K and 573 K. The properties were also similar to epoxy resin composites. The authors conclude that COPNA is worth studying for its heat-resistance properties. Three-dimensional moisture diffusion in graphite/epoxy laminates Blikstad, M. Journal of Reinforced Plastics and Composites Vol 5 No 1 (Janua O' 1986) pp 9-18 Graphite/epoxy specimens of varying configurations were used to investigate diffusivity to and along the fiber direction: they were exposed at RH of 70% and 98% at323 K. Diffusivity parallel to the fibres was approximately 10 times greater than generally found in laminates: this was due to the geometrical effect of the fibre orientation and the enhancement of diffusion along the fibre/matrix interface. The temperature dependence of diffusion (activation energy in an Arrhenius analysis) was lowest for diffusion along the fibre direction. A three-dimensional Fickian model for moisture absorption gave good agreement with experimental values. Wollastonite reinforced polypropylene composites: dynamic and steady state melt flow behaviour Shenoy. A.V. and Saini, D.R Journal of Reinforced Plastics and Composties Vol 5 No 1 (January 1986) pp 62-73 Dynamic and steady-state rheological properties of a composite of polypropylene and wollastonite were studied at 22l)°C: complex viscosity, storage modulus and loss modulus were measured over the frequency range 0.1-100 rad s 1, as well as the steady-shear viscosity. The experimentatl results were fitted to theoretical rheological predictions and allowed estimation of theological characteristics at different filler loadings.
OFI A2tIt Abstracts of British Patents are prepared by Dr F.R. Jones, Department of Ceramics, Glasses and Polymers, University of Sheffield, UK
UK PATENTS COMPONENTS Stackable long-term storage container, preferably for radioactive waste (Kernforschungszentrum Karlsruhe GmbH, FRG) GB 2 163 382,4 (20 February 1986) A GRP insert is used in a radioactive waste
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container to give corrosion protection.
Lightweight concrete roof tiles (The Marley Roof Tile Company, UK) GB2163 421A (26 February 1986) Concrete tiles with higher specific flexural strength are produced when a non-thixotropic silica fume (and dispersing agent) is included in the composition. Composite concrete huilding panel (McNeil, A. of Scotland) GB 2 164 072A
(12 March 1986) A panel consisting of acrylic acid copolymer modified G RC surfaces with a cellular concrete core is described. Polyacrylonitrile fiber with high strength and modulus (Japan Exlan Company Ltd, Japan) GB 2 165 484,4 (16 April 1986) The title fibre can be used as tyre-cord composites or as a carbon fibre precursor. It is spun
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